Once-through vapor generator



March 17, 1959 R. .QIANTSCHA AL 2,877,748

ONCE-THROUGH VAPOR GENERATOR Filed June 27, 1955 FIG. 2

IN VEN TORS ROBERT JANTSCHA BY JOHANN KOLLING ATTORNEY United StatesPatent O ON CE-THROUGH VAPOR GENERATOR Robert Jantscha and JohannKolling, Oberhausen, Germany, assignors to The Babcock & Wilcox Company,

New York, N. Y., a corporation of New Jersey Application June 27, 1955,Serial No. 518,182

2 Claims. (Cl. 122459) This invention relates to forced flow tubularboilers. In the generation of steam during forced flow through a gasheated tube system the greatest ditficulties are experienced in the partin which the last remnants of water are evaporated, the so calledtransition zone. It is known to protect this part by disposing it in aregion of rela tively low flue gas temperature. This, however, entailsdistributing the injurious effects over a larger heating surface. As analternative, feeding with surplus water and the use of a separator hasbeen adopted. The whole of the surplus water may be discharged if thepercentage used is not too great. Otherwise water is returned to thefeed pump. Since the separator makes a transition zone unnecessary, thedifficulties connected with such a zone are avoided.

The present invention includes the method of generating steam, accordingto which most of the water to be vaporized is evaporated and thegenerated steam is super heated in heat exchange means subjected to hotgases and the remainder of the water to be vaporized is evaporated byheat exchange with the superheated steam.

The invention also includes a forced flow, tubular v boiler comprising avaporizing stage exposed during operation to hot gases followed by asecond vaporizing stage arranged to operate with vapor generated andsuperheated in the unit as the heating medium.

The invention moreover includes a forced flow, once through, tubularboiler comprising a vaporizing stage exposed during operation to hotgases and adapted to effect most of the evaporation, followed by asecond vaporizing stage adapted to complete the evaporation and arrangedto operate with vapor generated and superheated in the unit as theheating medium.

By heating the transition zone with superheated steam the difiicultiesnormally experienced with a transition zone are to a great extenteliminated. Moreover, this solution possesses the advantage thatoperation may be either with or without surplus water.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawing and descriptivematter in which is illustrated and described a preferred embodiment ofthe invention.

In the drawings:

Figure 1 is a diagram illustrating the invention;

Figure 2 is a sectional elevation of a surface heat exchanger, a midportion being broken away; and

Figure 3 is a sectional plan view taken partly on the line 33 of Figure2.

Fig. 1 shows a steam economizer 1 discharging to a tube system 2 of asurface heat exchanger 4, the complementary element of which is apressure vessel enclosing the tube system. Between the outlet of thetube system 2' and the inlet to the vessel of the heat exchanger2,877,748 Patented Mar. 17, 1959 4 is connected the superheater 3, whilethe outlet from the vessel is connected to the superhcater 7.

During operation, the residual water content of the steam flowing fromthe steaming economizer 1 through the tube system 2' is evaporatedthrough heat exchange with superheated steam flowing from thesuperheater 3 through the vessel of the heat exchanger 4.

In Figures 2 and 3, which show a suitable form of surface heat exchangerfor use in the boiler of Figure l, a pressure vessel or tube shell 13comprises four tube sections 14, 15, 16 and 17 welded together, the tubesections 14, 15 and 17 being of somewhat greater diameter than the tubesection 16. The outer ends of the sections 14 and 17 are dished and areformed respectively with nozzles 18 and 19, while the sections 14 and 15are severally formed with nozzles 20 and 21.

The tube system 2' comprises a tube plate 22 welded to the tube section15 adjacent the weld between that section and tube section 14. Welded tothe tube plate 22 are the ends of tubes 23, arranged as a circular bank,and at their other ends the tubes are reduced in diameter and are weldedto a tube plate 24 of slightly less diameter than the tube section 16.At the side of the tube plate 24 remote from the tube bank is formed achamber by means of a hemispherical reversing hood 25 welded to the tubeplate and in communication with the chamber and extending through thetube plate 22 to the nozzle 18 constituted by the outer end thereof is acoaxial tube 26 Welded to the tube plates and to the tube section 14.The flow area through the tube 26 is approximately equal to the sum ofthe flow areas through the tubes 23.

The use of four tube sections in the formation of the pressure vesselhas been adopted in order to facilitate manufacture. During assembly,after the tube system comprising the tubes 23, 26, the tube plates 22,24 and the hood 25 and the tube sections 15, 16 and 17 have been weldedtogether, the tube system is introduced into the said tube sections andthe tube plate 22 is welded to the tube section 15. Finally, the tubesection 14 is placed in position and welded to the tube section 15 andthe end of tube 26.

In use, the nozzle 19 is connected to the steaming economizer 1 so thatthe steam and water mixture flows upwardly in the vessel 13 around thetubes 23 to the nozzle 21, which is connected to the superheater 3. Theoutlet from the superheater 3 is connected to the nozzle 20 so that thesuperheated steam flows downwardly through the tube 23 to the chamberbetween the tube plate 24 and the hood 25 and then on through the tube26 to the nozzle 18, which is connected to the superheater 7.

Generally, the direct contact heat exchanger or the surface heatexchanger will be arranged outside the boiler casing in proximity to thesections of heating surface associated therewith. In some instances aplurality of surface heat exchangers may be arranged in parallel withone another.

The invention may be applied to an existing force flow, once throughboiler having a transition zone by utilizing the transition zone asa'superheater of the steam which effects evaporation of the residualwater.

In the above description no mention has been made of the regulation ofthe supply of feed water, of heating, of constant water level or offinal steam temperature, as methods of effecting such regulation areknown.

While in accordance with the provisions of the statutes, there isillustrated and described herein specific embodiments of the invention,those skilled in the art will understand that changes may be made in theform of the invention covered by the claims, and that certain featuresof the invention may sometimes be used to advantage without acorresponding use of the other features.

What is claimed is:

1. In a once-through type vapor generator including a heat source, aconduit presenting heating surfaces wherein a vaporizable fluid isheated until there is a vapor-liquid mixture consisting of predominantlyvapor and the last remnants of liquid, an indirect heat exchanger out ofcontact with the heat source and arranged to receive said vapor-liquidmixture, a vapor super heater receiving heat from said source and havingits vapor inlet connected to one side of said heat exchanger, and meansfor passing superheated vapor from the exit of said superheater throughsaid heat exchanger to effect the complete evaporation of said lastremnants of liquid from said mixture and to also partially superheat theresulting vapor.

2. In a once-through type vapor generator including a heat source, aconduit presenting heating surfaces wherein a vaporizable fluid isheated until there is a vapor-liquid mixture consisting of predominantlyvapor and the last remnants of liquid, an indirect heat exchanger out ofcontact with the heat source and arranged to receive said vapor-liquidmixture, a primary vapor superheater receiving heat from said source andhaving its vapor inlet connected to one side of said heat exchanger,means for passing superheated vapor from the exit of said primarysuperheater through said heat exchanger to effect the completeevaporation of said last remnants of liquid from said mixture and toalso partially superheat the resulting vapor, and a secondarysuperheater in contact with the heat source and con nected to said heatexchanger for final heating of the vapor issuing from said primarysuperheater.

References Cited in the file of this patent UNITED STATES PATENTS

